1. Field of the Invention
This invention relates to a novel plastic slide having particular utility in epi-fluorescent microscopy. In particular, the plastic slide of the instant invention is composed of an optically opaque and substantially non-fluorescent composition.
2. Related Art
Epi-fluorescent microscopy, also referred to as incident fluorescent microscopy, is a well-known technique where a sample which is either fluorescent or is labeled with a fluorescent marker, is examined under radiation which induces fluorescence, typically ultraviolet radiation. The radiation excites the sample resulting in the sample fluorescing, thereby giving an indication of its presence, and to a certain extent its quantity. Epi-fluorescent microscopy has particular utility in the area of fluorimmunoassay and immunofluorometric assay.
Several problems exist with regard to epi-fluorescent microscopy. Initially, as discussed by James, "Light Microscopic Techniques in Biology and Medicine", pages 152-164 (1976) and by Locquin et al, "Handbook of Microscopy", pages 49-51 (1983), great care must be taken to ensure against background fluorescence, i.e., fluorescence arising not from the sample being tested but from exogenous sources such as the mounting medium, the immersion oil, the microscope objective, etc. The effect of background fluorescence will be either poor sample testing results or in the extreme, inaccurate results. Secondly, the yield in flux of fluorescent radiation arising from the tested sample is only of the order of 0.1% or even less of that emitted by the excitation radiation source (which is subsequently filtered out). However, because of the low flux of fluorescent radiation, it is sometimes difficult to detect this fluorescence. This problem is compounded by the fact that the radiation generated by the fluorescence is generated in all directions. Accordingly, unless blocked, a portion of the generated radiation will be directed upward in the general direction of the eyepiece (or other detection means) and a portion will be generally directed downward away from the eyepiece (or detection means). Obviously, the fluorescent radiation directed away from the eyepiece (or detection means) will escape detection thereby limiting even further the amount of fluorescent radiation subject to detection.
Glass microscope slides routinely employed in epi-fluorescent microscopy are advantageous insofar as such slides are not generally autofluorescent and therefore will not contribute to background fluorescence. However, on the negative side, glass slides do transmit visible radiation which is generally the fluorescent radiation of importance in epi-fluorescent microscopy. As such, that portion of the fluorescent radiation which is transmitted away from the detection means will not be subject to detection. Moreover, as is well apparent, glass slides are subject to breakage prior to and during sample observation. Breakage occurs most often during sample shipment and/or transportation but may also occur during slide preparation or sample observation. Breakage is a serious safety hazard because certain biohazards, i.e., viruses, bacteria, etc., contained in the test sample on the slide, may upon slide breakage expose the person handling the broken pieces of slide(s) to the biohazard. This problem is compounded by the fact that broken glass is frequently in a form which facilitates puncture and/or cuts to the handler and thereby increasing the handler's exposure risks. Accordingly, this breakage problem requires an increased level of care in slide preparation, shipment and sample observation. Therefore, it would be desirable to find a substitute for glass slides in epi-fluorescent microscopy. Such a substitute should preferably be non-fluorescent so as not to contribute to background fluorescence and should be optically opaque so as to prevent transmission of visible fluorescent radiation away from the detection means. Even more preferably, the optically opaque and substantially non-fluorescent slide should be resistant to the solvent employed in the test sample so as to prevent undo degradation of the slide and should be made of not easily breakable material. What I have found and what the instant invention is directed toward is a plastic slide which is optically opaque and substantially non-fluorescent. In a preferred embodiment, the plastic slide of this invention is additionally non-breakable and solvent-resistant.
Plastic slides are known in the art. For example, Malecki, U.S. Patent No. 4,587,213 discloses transparent plastic microscope slides prepared from materials such as celluloid, cellophane or urea formaldehyde resins or other synthetic resins such as cellulose acetate ethylcellulose, etc. Likewise, Muller, U.S. Pat. No. 4,427,889 discloses a microscope slide prepared from a copolymer of polyethylene and polypropylene. However, untreated plastic slides made from synthetic resins are autofluorescent and therefore not suitable for epi-fluorescent microscopy. Moreover, nothing in these references teaches the addition of any component which will render the plastic slide substantially non-fluorescent. Ornstein et al, U.S. Pat. No. 4,120,991, discloses the glass microscopic slides containing mounting mediums of hard synthetic resins. Scholefield, U.S. Pat. No. 4,094,745, discloses a fluorescent microscopy procedure which employs a carrier plate which can be a microscope slide, a plastic film or an opaque plate or strip. However, nothing in Scholefield teaches or suggests the type of opaque plate employed i.e., opaque glass or plastic, how the opaque plate is prepared, whether the opaque plate is substantially non-fluorescent, etc. Hartmann et al, Microsc.. Acta., Volume 81, No. 5, pages 407-409 (1979) discloses a slide for incident fluorescent microscopy, i.e., epifluorescent microscopy, which consists of placing a thin layer of black silicon rubber paste on a microscopic slide, placing the sample onto this silicon rubber paste and then placing a cover glass over the silicon rubber. The black silicon rubber is employed by Hartmann et al as an embedding or adhesion material. Accordingly, the slide of Hartmann et al is a "sandwich slide" wherein the sample on the silicon rubber is placed between the microscope slide on the bottom and a glass cover on the top.
Lastly, Cotten et al discloses stabilized polypropylene compositions wherein the polypropylene is stabilized against degradation by ultraviolet and visible light by the addition of heated treated carbon black. However, nothing in Cotten et al teaches or suggests that the addition of a sufficient amount of carbon black will render polypropylene non-fluorescent.